Despite advances in the surgical and catheter-based treatments for critical limb ischemia (CLI), 150,000 patients require lower limb amputation in the United States annually. Believing that an effective molecular therapy would have a significant clinical impact on the disability and limb loss rates in these patients, this study looks specifically at the role of endothelial nitric oxide synthase (eNOS) in collateral artery development (arteriogenesis). Because such development can reverse CLI, our central hypothesis maintains that the overexpression of eNOS will induce the ordered and sustainable development of collateral arteries in a way that will reverse CLI. Specifically, this research proposal aims 1) to identify the optimal gene transfer condition in a rat hind limb mode of ischemia; 2) to examine whether these eNOS gene transfer techniques can also reverse CLI clinically relevant animal models of diabetes, advanced age and hypercholesterolemia, and cigarette smoking; and 3) to characterize the molecular mechanisms by which eNOS overexpression increases arteriogenesis. To accomplish these aims, our research plan employs novel gene delivery techniques and sites of delivery. In particular, a unique method of intra-arterial gene transfer under vascular isolation that results in highly efficient and localized transgene expression will be used for gene transfer and laser Doppler perfusion imaging to measure dermal blood flow will facilitate the accomplishment of the above aims. Understanding the mechanisms by which eNOS exerts its powerful effects on arteriogenesis should provide additional insight into the fundamental mechanisms regulating arteriogenesis, and therefore open new therapeutic approaches for the treatment of CLI and other vascular diseases.